Many different machines and vehicles use either rigid linkage assemblies, such as control rods and tubes, or flexible linkage assemblies, such as push-pull control cables. Rigid linkages are typically used to attach manual shifters on vehicles (such as in automobiles, trucks or maintenance and construction vehicles) to the mechanism that is being shifted or moved (e.g. to gears, brakes, hydraulic valves, steering systems or control arms for moving scoops, hoes, plows, etc.). Other linkage assemblies are used on non-vehicular machines such as medical equipment and packing machinery.
The linkage assembly typically includes at least one rod or cable with one or two ends; each end is attached to a specific purpose end connector. These end connectors can have yokes (or clevises), ball joints, spherical rod ends, grooves, slots, hooks or any other shape or structure for attaching to further machinery. The rod or cable is typically threaded on its ends for attachment to the connector ends. The total length of the linkage assembly is set by threading a certain length of rod or cable into the end connectors.
These linkage assemblies must be a particular length between its ends in order to provide a specific amount of movement in a certain direction on one end of the assembly produced by moving the linkage assembly on its other end. If the linkage assembly is too long or too short, it may work inefficiently or badly, may not work at all, or it may require an uncomfortable or awkward amount of pressure or “feel” on linkage systems that are manipulated by hand or foot.
The conventional linkage assembly, however, must be assembled with the end connectors in order to determine if the correct length for the linkage assembly has been established. When the end connector is not free to rotate due to its attachment to the further machinery, the end connector must be de-installed from the machinery in order to adjust (thread or unthread) the length of the linkage assembly or a turnbuckle function is required. Traditional turnbuckle designs require a turnbuckle member as a separate component which is in turn attached directly to the linkage ends, or to a threaded rod or tube which is in turn connected to the linkage ends. Adjustment in this design can be provided but only by loosening at least two nuts and adjusting the turnbuckle component. FIG. 1 shows such a traditional design.
In addition, when the end connector must be in a certain orientation relative to the further machinery it is attaching to (e.g. a clevis connector end attaching to a pin held at a certain angle on the machine), the end connector can only be turned 180 or 360 degrees for threading on the control cable or rod for adjusting length. In other words, the end connector type in the case of the clevis or yoke that attaches to a pin limits the threading to a ½ or full turn. The end connector cannot be turned in increments between ½ and full turns. Similarly, ball joints with extension rods that must face a certain direction can only be turned one full turn.
Referring to FIG. 1, in some cases, these problems were solved with the common turnbuckle 100 which is a cylindrical bar 102 with interior threading (not shown) on both ends. A separate rod 104, 106 extends from each end of the bar 102 to provide a continuous linkage between end connectors 108, 102. Turning the bar 102 adjusts rods 104, 106 in or out of the bar 102 due to the threads, which changes the total length of the control device from the far ends of each rod. The jam nuts 110, 112 hold the position of the turnbuckle on each side, and must be loosened each time an assembly length change is desired.
The turnbuckle 102, however, must have one end with left hand threading while the other end has right hand threading. Thus, the adjustment requires three motions, the rotation of the turnbuckle and the rotation of the jam nuts on either end of the turnbuckle. At least two of these rotations are in opposite directions. This makes the adjustment procedure awkward and time consuming.
Referring to FIGS. 2–4, alternative solutions are presented by linkages 200, 300, and 400 disclosed by U.S. Pat. No. 5,529,316 issued to Mattila. Referring to FIG. 2, a linkage assembly 200 with a dual jam nut configuration is used where a single rod or cable 202 extends from one end connector 204 to another end connector 206. In this case, however, each end of the rod or cable 202 is threaded for adjustment with the respective end connector 204, 206. A jam nut 208, 210 is tightened against the end connectors respectively to hold the end connectors in place. In order to change the length of the linkage assembly, the jam nuts 208, 210 are loosened and the rod 202 is rotated until the desired length from end connector to end connector is established. The jam nuts are then retightened. This solution, however, is like the turnbuckle solution and requires opposite rotation of two jam nuts as well as rotation of the control rod 202.
Referring to FIG. 3, in yet another solution, a linkage assembly 300 has a single jam nut configuration with a single separate end connector 302 threaded to a rod 304 and fixed by a single jam nut 306. The opposite end 308 of the rod 304 has an integrally formed end connector 310. While this configuration eliminates the need to tighten two jam nuts, it requires that at least one of the end connectors 302, 310 be detached or de-installed from the machinery in order to have a free end to rotate for threading/unthreading to adjust the length of the assembly.
Referring to FIG. 4, a solution to the problems presented in the turnbuckle and duel and single jam nut configurations is presented by linkage assembly 400. This configuration includes a rod end 402 with a cylindrical head 404 that is axially fixed in an unthreaded bore 406 of an end connector 408. A threaded cover nut 410 traps the head 404 within the base, and the end connector 408 is threaded on its exterior for mating with a cylindrical portion 412 of the cover nut 410. An interior side of the cylindrical portion is threaded for this purpose. The cover nut 410 permits the rod 402 to rotate freely through an aperture 414 while preventing of the cylindrical head 404 from escaping the bore 406.
With this configuration, the length of the assembly 400 can only be adjusted on the opposite threaded end 416 relative to the bore end 402. This is disadvantageous because depending on the position of the linkage assembly 400 in a machine, it may be extremely difficult to adjust the length of the assembly on just one end where structure of the machine is in the way of adjustment tools.
In addition, this configuration also has the risk of the cover nut 410 loosening, which would then permit the rod 404 to move axially, changing the length of the linkage assembly 400.